Catalytically active particulate filter

ABSTRACT

The present invention relates to a particulate filter which comprises a wall flow filter of length L and three mutually different catalytically active coatings X, Y and Z, wherein the wall flow filter comprises channels E and A that extend in parallel between a first and a second end of the wall flow filter and are separated by porous walls forming surfaces OE and, respectively, OA, and wherein the channels E are gas-tightly sealed at the second end and the channels A are gas-tightly sealed at the first end, characterized in that the coating X is located in the porous walls, the coating Y is located in the channels E on the surfaces OE and the coating Z is located in the channels A on the surfaces OA.

The present invention relates to a catalytically active particulatefilter that is particularly suitable for the removal of particles,carbon monoxide, hydrocarbons and nitrogen oxides from the exhaust gasof internal combustion engines fueled by a stoichiometric air-fuelmixture.

Exhaust gases from combustion engines, i.e. gasoline engines, fueled bystoichiometric air-fuel mixtures are cleaned in conventional methodswith the aid of three-way catalytic converters. Such catalyticconverters are capable of simultaneously converting the three majorgaseous pollutants of the engine, namely hydrocarbons, carbon monoxideand nitrogen oxides, into harmless components.

In addition to such gaseous pollutants, the exhaust gas from gasolineengines also contains extremely fine particles (PM), which arise fromthe incomplete combustion of the fuel and essentially consist of soot.In contrast to the particle emission of diesel engines, the particles inthe exhaust gas of stoichiometrically operated gasoline engines are verysmall and have an average particle size of less than 1 μm. Typicalparticle sizes range from 10 to 200 nm. Furthermore, the amount ofparticles emitted is very low and ranges from 2 to 4 mg. The Europeanexhaust emission standard EU-6c is associated with a conversion of thelimit value for such particles from the particle mass limit value to amore critical particle number limit value of 6×10¹¹/km (in the WorldwideHarmonized Light Vehicles Test Cycle—WLTP). This creates a need forexhaust gas cleaning concepts for stoichiometrically operated combustionengines, which include effectively operating equipment for removingparticles.

Wall flow filters made of ceramic materials, such as silicon carbide,aluminum titanate and cordierite, have proven themselves in the field ofcleaning exhaust gases from lean-burn engines, i.e. in particular dieselengines. These wall flow filters are made up of a large number ofparallel channels formed by porous walls. The channels are alternatelysealed in a gas-tight manner at one of the two ends of the filter sothat channels A, which are open at the first side of the filter andsealed at the second side of the filter, and channels B, which aresealed at the first side of the filter and open at the second side ofthe filter, are formed. For example, exhaust gas flowing into channels Acan only leave the filter via channels B, and must flow through theporous walls between channels A and B for this purpose. When the exhaustgas passes through the wall, the particles are retained and the exhaustgas is cleaned. The particles retained in this manner must then be burntoff or oxidized in order to prevent a clogging of the filter or anunacceptable increase in the back pressure of the exhaust system. Forthis purpose, the wall flow filter is, for example, provided withcatalytically active coatings that reduce the ignition temperature ofsoot.

Applying such coatings to the porous walls between the channels(so-called “on-wall coating”) or introducing them into the porous walls(so-called “in-wall coating”) is already known. EP 1 657 410 A2 alsoalready describes a combination of both coating types; that is, part ofthe catalytically active material is present in the porous walls andanother part is present on the porous walls.

The concept of removing particles from the exhaust gas using wall flowfilters has already been applied to the cleaning of exhaust gas fromgasoline engines operated with stoichiometric air-fuel mixtures; see,for example, EP 2042226 A2. According to its teaching, a wall flowfilter comprises two layers arranged one above the other, wherein onecan be arranged in the porous wall and the other can be arranged on theporous wall.

DE 102011050788 A1 pursues a similar concept. There, the porous filterwalls contain a catalyst material of a three-way catalytic converter,while the partition walls additionally comprise a catalyst material of athree-way catalytic converter in the respective end sections, both onthe inflow side and on the outflow side.

FR 3 020 091 A1 discloses a particulate filter that comprises a coatingin the porous walls along with coatings on the surfaces of the inlet andoutlet channels. The latter extend over a partial area of the filterlength, both on the inlet and outlet surfaces on the side of the filterat which the exhaust gas enters.

There is still a need for catalytically active particulate filters thatcombine the functionalities of a particulate filter and a three-waycatalytic converter and at the same time adhere to the limits that willapply in the future.

The present invention relates to a particulate filter which comprises awall flow filter of length L and three mutually different coatings X, Yand Z, wherein the wall flow filter comprises channels E and A thatextend in parallel between a first and a second end of the wall flowfilter and are separated by porous walls forming surfaces O_(E) andO_(A), respectively, and wherein the channels E are sealed in agas-tight manner at the second end and the channels A are sealed in agas-tight manner at the first end, characterized in that coating X islocated in the porous walls, coating Y is located in the channels E onthe surfaces O_(E) and coating Z is located in the channels A on thesurfaces O_(A).

The coatings X, Y and Z are catalytically active, especially atoperating temperatures of 250 to 1100° C. They are different from eachother, but all three usually contain one or more precious metals fixedto one or more substrate materials and one or more oxygen storagecomponents. The coatings X, Y and Z may differ in the components theycontain. For example, they may differ in terms of the precious metalsthey contain or the oxygen storage components they contain. However,they may also contain identical components, but such components mustthen be present in different quantities.

The coatings X, Y and Z preferably do not contain SCR catalysts,especially no metal-exchanged molecular sieves.

Platinum, palladium and rhodium are particularly suitable as preciousmetals, wherein palladium, rhodium or palladium and rhodium arepreferred.

The precious metals are usually used in quantities of 0.4 to 4 g/l basedon the volume of the wall flow filter.

As substrate materials for the precious metals, all materials familiarto the person skilled in the art can be considered for this purpose.Such materials are in particular metal oxides with a BET surface area of30 to 250 m²/g, preferably 100 to 200 m²/g (determined according to DIN66132). Particularly suitable substrate materials for the preciousmetals are selected from the series consisting of aluminum oxide, dopedaluminum oxide, silicon oxide, titanium dioxide and mixed oxides of oneor more of these.

Doped aluminum oxides are, for example, aluminum oxides doped withlanthanum oxide, zirconium oxide and/or titanium oxide.Lanthanum-stabilized aluminum oxide is advantageously used, whereinlanthanum is used in quantities of 1 to 10% by weight, preferably 3 to6% by weight, in each case calculated as La₂O₃ and based on the weightof the stabilized aluminum oxide.

Cerium/zirconium/rare earth metal mixed oxides are particularly suitableas oxygen storage components. The term “cerium/zirconium/rare earthmetal mixed oxide” within the meaning of the present invention excludesphysical mixtures of cerium oxide, zirconium oxide and rare earth oxide.Rather, “cerium/zirconium/rare earth metal mixed oxides” arecharacterized by a largely homogeneous, three-dimensional crystalstructure that is ideally free of phases of pure cerium oxide, zirconiumoxide or rare earth oxide. Depending on the manufacturing process,however, not completely homogeneous products may arise which cangenerally be used without any disadvantage.

In all other respects, the term “rare earth metal” or “rare earth metaloxide” within the meaning of the present invention does not includecerium or cerium oxide.

Lanthanum oxide, yttrium oxide, praseodymium oxide, neodymium oxideand/or samarium oxide can, for example, be considered as rare earthmetal oxides in the mixed cerium/zirconium/rare earth metal mixedoxides.

Lanthanum oxide, yttrium oxide and/or praseodymium oxide are preferred.Lanthanum oxide and/or yttrium oxide are particularly preferred, andlanthanum oxide and yttrium oxide, yttrium oxide and praseodymium oxide,and lanthanum oxide and praseodymium oxide are more particularlypreferred.

In accordance with the invention, the ratio of cerium oxide to zirconiumoxide in the cerium/zirconium/rare earth metal mixed oxides can varywithin wide limits. It amounts to, for example, 0.1 to 1.0, preferablyfrom 0.2 to 0.7, more preferably from 0.3 to 0.5.

The oxygen storage components are usually used in quantities of 50 to120 g/l based on the volume of the wall flow filter.

In the embodiments of the present invention, one or more of the coatingsX, Y and Z contain an alkaline earth compound, such as barium oxide orbarium sulfate, Preferred embodiments contain barium sulfate in thecoatings X and Y. The amount of barium sulfate per coating particularlyamounts to 5 to 20 g/l of the volume of the wall flow filter.

In further embodiments of the present invention, one or more of thecoatings X, Y and Z contain additives, such as rare earth compounds,such as lanthanum oxide, and/or binders, such as aluminum compounds.Such additives are used in quantities that can vary within wide limitsand that the person skilled in the art can determine in the specificcase by simple means.

In embodiments of the present invention, the coating X compriseslanthanum-stabilized aluminum oxide, palladium or palladium and rhodium,a first oxygen storage component comprising zirconium oxide, ceriumoxide, yttrium oxide and lanthanum oxide, and a second oxygen storagecomponent comprising zirconium oxide, cerium oxide, yttrium oxide andpraseodymium oxide. The coating X preferably compriseslanthanum-stabilized aluminum oxide in quantities of 20 to 40% byweight, more preferably 25 to 30% by weight, based on the total weightof the coating X. The coating X preferably comprises each of the twooxygen storage components in amounts of 25 to 35% by weight based on thetotal weight of the coating X.

In embodiments of the present invention, the coating X extends over theentire length L of the wall flow filter. The loading of the wall flowfilter with coating X preferably amounts to 25 to 150 g/l based on thevolume of the wall flow filter.

In embodiments of the present invention, the coating Y compriseslanthanum-stabilized aluminum oxide, palladium or palladium and rhodiumand an oxygen storage component comprising zirconium oxide, ceriumoxide, lanthanum oxide and praseodymium oxide.

The coating preferably comprises X lanthanum-stabilized aluminum oxidein quantities of 30 to 60% by weight, more preferably 40 to 50% byweight, based on the total weight of the coating Y. The coating Ypreferably comprises the oxygen storage component in quantities of 30 to60% by weight, more preferably 40 to 50% by weight, based on the totalweight of the catalytically active coating Y.

In embodiments of the present invention, the coating Y extends from thefirst end of the wall flow filter over 20 to 70%, preferably 25 to 61%,of the length L of the wall flow filter. The loading of the wall flowfilter with coating Y preferably amounts to 50 to 70 g/l based on thevolume of the wall flow filter.

In embodiments of the present invention, the coating Z compriseslanthanum-stabilized aluminum oxide, palladium or palladium and rhodiumand an oxygen storage component comprising zirconium oxide, ceriumoxide, lanthanum oxide and yttrium oxide.

The coating Z preferably comprises lanthanum-stabilized aluminum oxidein quantities of 40 to 65% by weight, more preferably 50 to 60% byweight, based on the total weight of the coating Z. The coating Zpreferably comprises the oxygen storage component in quantities of 30 to60% by weight, more preferably 40 to 50% by weight, based on the totalweight of the coating Z.

In embodiments of the present invention, the coating Z extends from thesecond end of the wall flow filter over 20 to 70%, preferably 25 to 61%,of its length L. The loading of the wall flow filter with coating Zpreferably amounts to 50 to 70 g/l based on the volume of the wall flowfilter.

In embodiments of the present invention, the sum of the lengths ofcoatings Y and Z is less than the total filter length L, preferably≤90%, more preferably ≤80%, of the total filter length L.

In one embodiment of the present invention, the present inventionrelates to a particulate filter which comprises a wall flow filter oflength L and three mutually different coatings X, Y and Z, wherein thewall flow filter comprises channels E and A that extend in parallelbetween a first and a second end of the wall flow filter and areseparated by porous walls forming surfaces O_(E) and O_(A),respectively, and wherein the channels E are sealed in a gas-tightmanner at the second end and the channels A are sealed in a gas-tightmanner at the first end, characterized in that

-   -   the coating X is located in the porous walls, extends over the        entire length L of the wall flow filter, and contains        lanthanum-stabilized aluminum oxide in an amount of 25 to 30% by        weight based on the total weight of the coating X, palladium or        palladium and rhodium, a first oxygen storage component        comprising zirconium oxide, cerium oxide, yttrium oxide and        lanthanum oxide in an amount of 25 to 35% by weight based on the        total weight of the coating X, and a second oxygen storage        component comprising zirconium oxide, cerium oxide, yttrium        oxide and praseodymium oxide in an amount of 25 to 35% by weight        based on the total weight of the coating X, and    -   the coating Y is located in the channels E on the surfaces        O_(E),    -   extends from the first end of the wall flow filter to 25 to 75%        of its length L and contains lanthanum-stabilized aluminum oxide        in an amount of 40 to 50% by weight based on the total weight of        the coating Y, palladium or palladium and rhodium and an oxygen        storage component comprising zirconium oxide, cerium oxide,        lanthanum oxide and praseodymium oxide in an amount of 40 to 50%        by weight based on the total weight of the coating Y, and    -   the coating Z is located in the channels A on the surfaces        O_(A), extends from the second end of the wall flow filter to 25        to 75% of its length L and contains lanthanum-stabilized        aluminum oxide in an amount of 50 to 60% by weight based on the        total weight of the coating Z, palladium or palladium and        rhodium and an oxygen storage component comprising zirconium        oxide, cerium oxide, lanthanum oxide and yttrium oxide in an        amount of 40 to 50% by weight based on the total weight of the        coating Z.

Wall flow filters that can be used in accordance with the presentinvention are well-known and available on the market, They consist of,for example, silicon carbide, aluminum titanate or cordierite, and have,for example, a cell density of 200 to 400 cells per inch and usually awall thickness between 6 and 12 mil, or 0.1524 and 0.305 millimeters.

In the uncoated state, they have porosities of 50 to 80, in particular55 to 75%, for example. Their average pore size in the uncoated stateamounts to 10 to 25 micrometers, for example. As a rule, the pores ofthe wall flow filter are so-called “open pores;” that is, they have aconnection to the channels. In addition, the pores are usuallyinterconnected with one another. This allows, on the one hand, easycoating of the inner pore surfaces and, on the other hand, easy passageof the exhaust gas through the porous walls of the wall flow filter.

The particulate filter in accordance with the invention can be producedaccording to methods known to the person skilled in the art, for exampleby applying a coating suspension, which is usually called a washcoat, tothe wall flow filter by means of one of the usual dip coating methods orpump and suction coating methods. Thermal post-treatment or calcinationusually follow. The coatings X, Y and Z are obtained in separate andsuccessive coating steps.

The person skilled in the art knows that the average pore size of thewall flow filter and the average particle size of the catalyticallyactive materials must be matched to each other in order to achieve anon-wall coating or an in-wall coating. In the case of an in-wallcoating, the average particle size of the catalytically active materialsmust be small enough to penetrate the pores of the wall flow filter. Incontrast, in the case of an on-wall coating, the average particle sizeof the catalytically active materials must be large enough not topenetrate the pores of the wall flow filter.

In embodiments of the present invention, the coating suspension for theproduction of the coating X is ground up to a particle size distributionof d₅₀=1 to 3 μm and d₉₉=9 to 5 μm. In embodiments of the presentinvention, the coating suspension for the production of the coating Y isground up to a particle size distribution of d₅₀=4 to 8 μm and d₉₉=22 to16 μm; In embodiments of the present invention, the coating suspensionfor the production of the coating Z is ground up to a particle sizedistribution of d₅₀=4 to 8 μm and d₉₉=22 to 16 μm.

FIG. 1 shows a particulate filter in accordance with the invention whichcomprises a wall flow filter of length L (1) with channels E (2) andchannels A (3) extending in parallel between a first end (4) and asecond end (5) of the wall flow filter and separated by porous walls (6)forming surfaces O_(E) (7) and O_(A) (8), respectively, and wherein thechannels E (2) are sealed in a gas-tight manner at the second end (5)and the channels A (3) are sealed in a gas-tight manner at the first end(4). The coating X is located in the porous walls (6), the coating Y (9)is located in the channels E (2) on the surfaces O_(E) (7) and thecoating Z (10) is located in the channels A (3) on the surfaces O_(A)(8).

The invention is explained in more detail in the following examples.

COMPARATIVE EXAMPLE 1

Aluminum oxide stabilized with 4% by weight lanthanum oxide and acerium/zirconium mixed oxide with a cerium oxide content of 40% byweight were suspended in water. The suspension thus obtained was thenmixed with a palladium nitrate solution and a rhodium nitrate solutionunder constant stirring. The resulting coating suspension was useddirectly to coat a commercially available wall flow filter substrate. Inthis case, the coating suspension was introduced into the filter wallsof the substrate. The coated filter thus obtained was dried and thencalcined.

The total load of the filter VGPF1 thus obtained amounted to 125 g/l,the total precious metal load amounted to 2.58 g/l with a ratio ofpalladium to rhodium of 5.1:1.

COMPARATIVE EXAMPLE 2

a) Aluminum oxide stabilized with 4% by weight lanthanum oxide and acerium/zirconium mixed oxide with a cerium oxide content of 33% byweight were suspended in water. The suspension thus obtained was thenmixed with a palladium nitrate solution and a rhodium nitrate solutionunder constant stirring. The resulting coating suspension was useddirectly to coat a commercially available wall flow filter substrate. Inthis case, the coating suspension was introduced into the filter wallsof the substrate. The coated filter thus obtained was dried and thencalcined.

The total load of this layer amounted to 100 g/l; the total preciousmetal load amounted to 2.05 g/l with a ratio of palladium to rhodium of3.9:1.

b) Aluminum oxide stabilized with 4% by weight lanthanum oxide andcerium/zirconium mixed oxide with a cerium oxide content of 40% byweight were suspended in water. The suspension thus obtained was thenmixed with a palladium nitrate solution under constant stirring. Theresulting coating suspension was used directly to coat the wall flowfilter substrate obtained in a) above. In this case, the coatingsuspension was applied with a load of 57 g/l to the wall surfaces onlyin the inflow channels over a length of 25% of the total length. Thecoated filter thus obtained was dried and then calcined.

The total precious metal load of the filter VGPF2 thus obtained amountedto 2.58 g/l with a ratio of palladium to rhodium of 5:1.

EXAMPLE 1

a) Aluminum oxide stabilized with 4% by weight lanthanum oxide andcerium/zirconium mixed oxide with a cerium oxide content of 33% byweight were suspended in water. The suspension thus obtained was thenmixed with a palladium nitrate solution and a rhodium nitrate solutionunder constant stirring. The resulting coating suspension was useddirectly to coat a commercially available wall flow filter substrate. Inthis case, the coating suspension was introduced into the filter wallsof the substrate. The coated filter thus obtained was dried and thencalcined.

The total load of this layer amounted to 100 g/l; the total preciousmetal load amounted to 1.93 g/l with a ratio of palladium to rhodium of4.7:1.

b) The coated wall flow filter obtained according to a) was providedwith a second coating as specified in comparative example 2, step b).

c) Aluminum oxide stabilized with 4% by weight lanthanum oxide andcerium/zirconium mixed oxide with a cerium oxide content of 24% byweight were suspended in water. The suspension thus obtained was thenmixed with a palladium nitrate solution and then with a rhodium nitratesolution under constant stirring. The resulting coating suspension wasused directly to coat the wall flow filter substrate obtained in stepb). In this case, the coating suspension was applied with a load of 54g/l to the wall surfaces over a length of 25% of the total length onlyin the still uncoated outflow channels of the substrate. The coatedfilter thus obtained was dried and then calcined.

The total precious metal load of the filter GPF1 thus obtained amountedto 2.58 g/l with a ratio of palladium to rhodium of 5:1.

EXAMPLE 2

Example 1 was repeated with the difference that cerium/zirconium mixedoxide was not used in step b).

The total precious metal load of the filter GPF2 thus obtained amountedto 2.58 g/l with a ratio of palladium to rhodium of 5:1.

Catalytic Characterization

The catalytically active particulate filters VGPF1, VGPF2, GPF1 and GPF2were each tested in the fresh state and the aged state in the “lambdasweep test.”

The particulate filters were aged together in an engine test bench agingprocess. This aging process consists of an overrun cut-off aging processwith an exhaust gas temperature of 950° C. before the catalyst inlet(maximum bed temperature of 1030° C.). The aging time amounted to 76hours.

Following aging, a part of each of the particulate filters VGPF1, VGPF2,GPF1 and GPF2 was loaded with 5 g/l soot on an engine test bench.

Subsequently, an engine test bench was used to test the startingbehavior at a constant average air ratio λ, and the dynamic conversionupon a change to λ was examined.

The following tables contain the temperatures T₅₀ at which 50% of thecomponent under consideration is converted. In this case, the startingbehavior with stoichiometric exhaust gas composition (λ=0.999 with ±3.4%amplitude) was determined.

Table 1 contains the data for the fresh particulate filters, Table 2contains the data for the aged particulate filters and Table 3 containsthe data for the particulate filters loaded with soot.

TABLE 1 T₅₀ HC stoichio- T₅₀ CO stoichio- T₅₀ NOx stoichio- metricmetric metric VGPF1 260 254 257 VGPF2 251 243 246 GPF1 252 240 245 GPF2246 234 237

TABLE 2 T₅₀ HC stoichio- T₅₀ CO stoichio- T₅₀ NOx stoichio- metricmetric metric VGPF1 415 439 429 VGPF2 404 424 418 GPF1 402 416 412 GPF2403 422 416

TABLE 3 T₅₀ HC stoichio- T₅₀ CO stoichio- T₅₀ NOx stoichio- metricmetric metric VGPF1 392 403 402 VGPF2 390 399 401 GPF1 385 394 395 GPF2385 394 397

The dynamic conversion behavior of the particulate filters wasdetermined in a range for λ from 0.99 to 1.01 at a constant temperatureof 510° C. The amplitude of λ in this case amounted to ±3.4%, Table 4shows the conversion at the intersection of the CO and NOx conversioncurves, along with the associated HO conversion of the aged particulatefilters. Table 5 shows the corresponding points of the filters loadedwith soot.

TABLE 4 CO/NOx conversion at HC conversion at the λ of the intersectionthe CO/NOx intersection VGPF1 64% 94% VGPF2 72% 95% GPF1 78% 95% GPF272% 95%

TABLE 5 CO/NOx conversion at HC conversion at the λ of the intersectionthe CO/NOx intersection VGPF1 69% 95% VGPF2 78% 96% GPF1 85% 96% GPF280% 95%

In comparison to VGPF1 and VGPF2, the particulate filters GPF1 and GPF2in accordance with the invention show a clear improvement in startingbehavior and dynamic CO/NOx conversion, both in the fresh state and inthe aged state with and without additionally applied soot.

1. Particulate filter for removing particulates, carbon monoxide,hydrocarbons and nitrogen oxides from the exhaust gas of internalcombustion engines operated with a stoichiometric air-fuel mixture,which particulate filter comprises a wall flow filter of length L andthree mutually different coatings X, Y and Z, wherein the wall flowfilter comprises channels E and A that extend in parallel between afirst and a second end of the wall flow filter and are separated byporous walls forming surfaces O_(E) and O_(A), respectively, and whereinthe channels E are sealed in a gas-tight manner at the second end andthe channels A are sealed in a gas-tight manner at the first end,characterized in that coating X is located in the porous walls, coatingY is located in the channels E on the surfaces O_(E) and coating Z islocated in the channels A on the surfaces O_(A).
 2. Particulate filterin accordance with claim 1, wherein the coating X extends over theentire length L of the wall flow filter.
 3. Particulate filter inaccordance with claim 1, wherein the coating Y extends from the firstend of the wall flow filter over 20 to 70% of the length L of the wallflow filter.
 4. Particulate filter in accordance with claim 1, whereinthe catalytically active coating Z extends from the second end of thewall flow filter over 20 to 70% of the length L of the wall flow filter.5. Particulate filter in accordance with claim 3, wherein the sum of thelengths of the coatings Y and Z is less than the total filter length L.6. Particulate filter in accordance with claim 1, wherein each of thecoatings X, Y and Z contains one or more precious metals fixed on one ormore substrate materials and one or more oxygen storage components. 7.Particulate filter in accordance with claim 6, wherein each of thecoatings X, Y and Z contains the precious metals platinum, palladiumand/or rhodium.
 8. Particulate filter in accordance with claim 6,wherein each of the coatings X, Y and Z contains the precious metalspalladium, rhodium or palladium and rhodium.
 9. Particulate filter inaccordance with claim 6, wherein the substrate materials for theprecious metals are metal oxides with a BET surface area of 30 to 250m²/g (determined according to DIN 66132).
 10. Particulate filter inaccordance with claim 6, wherein the substrate materials for theprecious metals are selected from the series consisting of aluminumoxide, doped aluminum oxide, silicon oxide, titanium dioxide and mixedoxides of one or more of these.
 11. Particulate filter in accordancewith claim 6, wherein the coatings X, Y and Z containcerium/zirconium/rare earth metal mixed oxides as oxygen storagecomponents.
 12. Particulate filter in accordance with claim 11, whereinthe cerium/zirconium/rare earth metal mixed oxides contain lanthanumoxide, yttrium oxide, praseodymium oxide, neodymium oxide and/orsamarium oxide as rare earth metal oxide.
 13. Particulate filter inaccordance with claim 11, wherein the cerium/zirconium/rare earth metalmixed oxides contain lanthanum oxide and yttrium oxide, yttrium oxideand praseodymium oxide or lanthanum oxide and praseodymium oxide as rareearth metal oxide.
 14. Particulate filter in accordance with claim 1,wherein the coating X contains lanthanum-stabilized aluminum oxide,palladium or palladium and rhodium, a first oxygen storage componentcomprising zirconium oxide, cerium oxide, yttrium oxide and lanthanumoxide, and a second oxygen storage component comprising zirconium oxide,cerium oxide, yttrium oxide and praseodymium oxide.
 15. Particulatefilter in accordance with claim 1, wherein the coating Y containslanthanum-stabilized aluminum oxide, palladium or palladium and rhodiumand an oxygen storage component comprising zirconium oxide, ceriumoxide, lanthanum oxide and praseodymium oxide.
 16. Particulate filter inaccordance with claim 1, wherein the coating Z containslanthanum-stabilized aluminum oxide, palladium or palladium and rhodiumand an oxygen storage component comprising zirconium oxide, ceriumoxide, lanthanum oxide and yttrium oxide.
 17. Particulate filter inaccordance with claim 1, wherein the coating X is located in the porouswalls, extends over the entire length L of the wall flow filter, andcontains lanthanum-stabilized aluminum oxide in an amount of 25 to 30%by weight based on the total weight of the coating X, palladium orpalladium and rhodium, a first oxygen storage component comprisingzirconium oxide, cerium oxide, yttrium oxide and lanthanum oxide in anamount of 25 to 35% by weight based on the total weight of the coatingX, and a second oxygen storage component comprising zirconium oxide,cerium oxide, yttrium oxide and praseodymium oxide in an amount of 25 to35% by weight based on the total weight of the coating X, and thecoating Y is located in the channels E on the surfaces O_(E), extendsfrom the first end of the wall flow filter to 25 to 75% of its length Land contains lanthanum-stabilized aluminum oxide in an amount of 40 to50% by weight based on the total weight of the coating Y, palladium orpalladium and rhodium and an oxygen storage component comprisingzirconium oxide, cerium oxide, lanthanum oxide and praseodymium oxide inan amount of 40 to 50% by weight based on the total weight of thecoating Y, and the coating Z is located in the channels A on thesurfaces O_(A), extends from the second end of the wall flow filter to25 to 75% of its length L and contains lanthanum-stabilized aluminumoxide in an amount of 50 to 60% by weight based on the total weight ofthe coating Z, palladium or palladium and rhodium and an oxygen storagecomponent comprising zirconium oxide, cerium oxide, lanthanum oxide andyttrium oxide in an amount of 40 to 50% by weight based on the totalweight of the coating Z.